The present invention relates to a method for detecting short-circuits in circuit branches of electrical power system networks. A device implementing the method applies a test voltage to the circuit branch being tested and then measures the resulting current. The measured current is then supplied to an evaluation circuit which compares the actual-value to a predetermined setpoint-value.
Circuit-breakers are usually used for switching electrical branches to a system circuit. Existing circuit breakers are most commonly stressed when a short-circuited branch is brought into the system circuit, for example during the initial operation of a defective system. This problem results from the fact that the breaking operation takes place only after the switch has first terminated its closing operation. As a result, the duration of the short-circuit becomes quite considerable. In addition, when a short circuited branch is brought into a circuit, the resistance of the resulting entire circuit becomes very low. As a result of this low resistance, the short-circuit current is high.
The design tolerances of a circuit-breaker, in particular, but also of other operational equipment could be relaxed and, thus, such equipment could be made less expensive if the existence of a short-circuit in the branch could be automatically tested before the branch is connected to the system circuit. If the branch is short-circuited, it could then be prevented from being connected to the system circuit. The duration of such a test must be short enough so that any noticeable closing delay would be avoided, i.e., the duration of such a test must be more or less in the order of magnitude of less than one second.
The German Published Patent Application 36 26 399 discloses an arrangement for influencing, and more particularly for preventing a switching device (preferably a remote-controlled switching device) from closing. The operation of this arrangement depends upon data pertaining to power supply conditions. A separate-source voltage is injected onto a branch being tested. To inject the separate-source voltage, this arrangement provides an impulse generator to generate testing pulses. A downstream evaluation circuit compares an actual-value to a setpoint value and determines the peak value of the converted instantaneous electric power output. Furthermore, the German Published Patent Application 33 47 209 discloses an arrangement for influencing a switching device in which the impedance of the branch is determined and compared to preset values.
The previously known arrangements unequivocally and rapidly find short-circuits, interturn shorts in windings, and breaks in the supply lead. However, these arrangements are not well suited for detecting existing short-circuits in any power system network.
Thus, a method for detecting short-circuits in circuit branches of any power system network is needed as well as a circuit arrangement for implementing the method.